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The purpose of this work was to study the influence of acoustic cavitation on the oxidation of a mill bleached machine dried hardwood Kraft pulp. The oxidation of the pulp was carried out using 4-acetamido-TEMPO coupled with NaOCl/NaBr as co-oxidizer. The carboxylate content was increased by about 30% without any adverse impact on the degree of polymerization in the case of oxidations under acoustic cavitation compared to the reference without acoustic cavitation. A close correlation between the yield of nanocellulose and the carboxylate content of the oxidized pulps was observed. The individualized cellulose nanofibres were 3-4 nm in width and a few microns in length.

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The efficiency of cellulose oxidation mediated by the 4-acetamido-TEMPO radical under ultrasonic cavitation was investigated using two ultrasonic systems: a batch lab scale ultrasonic bath with a glass reactor and a semi-continuous flow-through sonoreactor. The main objective was to explore the possibility of scaling up the production of oxidized cellulose under ultrasound, from a lab scale process to a pilot plant process, which served as a precursor for producing nanofibrils cellulose. It was found that under acoustic cavitation, the efficiency of TEMPO-mediation oxidation of native cellulose was significantly improved, particularly in the flow-through sonoreactor. In comparison with the glass reactor, the flow-through sonoreactor reduce the applied energy by 88% while increasing 7.8 times the production rate of radicals. These results enable a possibility of producing oxidized fibers for industrial applications.

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